1. Field of the Invention
The present invention relates to a fuel injection controlling device for a two-cycle engine. More particularly, to a fuel injection controlling device for a two-cycle engine which employs an electronic fuel injection system.
2. Description of Background Art
A technique has been proposed for determining when an electronic fuel injection system (Fuel Injection) is to be applied to a two-cycle engine wherein a supply of fuel is responsive to an engine rotational speed Ne and a throttle opening .THETA.th has been proposed. The technique is disclosed, for example, in Japanese Patent Laid-Open No. 59-49337.
The technique described above has the following problems. As illustrated in FIG. 23, variation in throttle opening of a two-cycle engine and variations in amount of fuel to be supplied in response to such variation in throttle opening is set forth. Fuel injection amounts where a carburetor is used as the fuel injection system and where fuel injection is accomplished in response to an engine rotational speed Ne and a throttle opening .THETA.th are shown.
In a two-cycle engine, if the throttle opening .THETA.th is decreased, then the delivery ratio is decreased and consequently the engine will enter a misfire condition.
In a fuel injection system which employs a carburetor, when the throttle opening is small and the delivery ratio is low, fuel is not drafted to a large extent. Accordingly, even if the throttle valve is changed from a low opening condition to a high opening condition, a time lag occurs in the draft amount of fuel. Consequently, an amount of fuel which corresponds to an increase in throttle opening .THETA.th is not immediately supplied. Accordingly, unignited gas in a misfire condition returns to an appropriate air fuel ratio, and transition to a fired condition can be smoothly achieved.
On the other hand, in a fuel injection system which employs an injector which injects fuel in response to Ne and .THETA.th, a fuel injection amount determined in response to .THETA.th is injected immediately. Consequently, fresh air is further supplied to ignited gas in a misfire condition so that the air fuel ratio may be overrich. As a result, the engine may not change from a misfire condition to a fire condition. In particular, the amount of fuel injection is excessively large in a region indicated by oblique lines in FIG. 23.